The present invention relates generally to the fabrication of components for jet engines. More specifically, it relates to the fabrication of seals and flaps for use in jet engines at elevated temperatures in controlling flow of high temperature gas through the engine.
It is known that some parts of jet engines are subjected to high stress during engine startup or operation. Other parts of the jet engines are subjected to high temperature but are not subjected to high stress during either the startup or steady state operation of the engine. The mode of failure of components of jet engines such as flaps, seals, vanes, and the like, relates both to the material of which the component is composed and also the method of fabrication. The failure of seals and flaps is generally described in terms of thermal fatigue cracking, with degradation of performance related to edge distortion allowing cold air leakage.
In accordance with one mode of practice of the present invention, the performance of engine components may be improved by using combinations of materials and fabrication techniques which permit novel structures to be formed conveniently and economically.
It is highly desirable in the formation of components for jet engines to keep the weight and, accordingly, the bulk of the article at a level whichis sufficient to accomplish the task for which the part was prepared, over an extended useful life, but at the same time to minimize the weight of the part used in the jet engine. For this reason, generally it is desirable to have planar shaped parts, such as flaps and seals which have a minimum weight which permits the part to effectively accomplish its purpose over an extended useful life.
Parts which are employed in jet engines are generally fabricated of the so-called superalloys. These are alloys which resist softening and deformation at elevated use temperature. Temperatures of above 1000.degree. C. are involved in jet engine operation.
In some cases, it is desirable to have the planar parts made up of more than a single metal, as for example a bimetal structure in which two coextensive sheets are sandwiched together. This could be because different functional requirements are presented in respect to one face of the sheet relative to the other. Such requirements may be an ability of one face of the bimetal structure to withstand oxidation, for example.
A strong integral bond must exist between the two layers where two different metals are employed.
However, although two different metals are used in the formation of such sheet, the thickness of the sheet must, nevertheless, be minimized consistent with the functional restraint and requirements of the sheet in its application as a seal or flap. A prior art structure as used in jet engines as, for example, in a variable exhaust nozzle seal of a jet engine is a seal of 0.040" of wrought Rene 41 sheet metal.